The present invention relates to a process for producing high-purity magnesium hydroxide and for obtaining therefrom magnesium oxide by calcination.
Natural resources of magnesium hydroxide [CRN 1309-48-4] are rare so that this material is seldom mined. Nowadays, magnesium hydroxide is obtained by precipitation from seawater (cf. Gilpin, W. C. and Heasman, N., Chem. Ind. (London), 1977, p. 567-572; Drum, J. C., Tangney, S., Trans. J. Br. Ceramic Soc., 77 (1978), no. 4, p. 10-14) and precipitation from magnesium salt solutions using calcium hydroxide.
Said manufacturing processes have one disadvantage: the magnesium hydroxide produced in this way is hardly suitable for a large number of catalytic operations and for the production of special ceramics. This is primarily due to impurities in the form of other metals making the magnesium hydroxide particularly unsuitable for catalytic processes.
DE 3 244 972-C1 discloses a continuous process for producing high-purity aluminium alcoholates. According to said publication, aluminium metal is reacted with alcohol yielding aluminium alcoholate which can be liberated from other metals present in the aluminium metal by filtration and/or distillation because said metals are not converted or are only slowly converted into metal alcoholates. Up to now, however, said process has not been applicable to magnesium because the magnesium alcoholates known in the art are not liquid and, therefore, cannot be filtered.
Furthermore, they cannot be melted without undergoing decomposition and, consequently, cannot be distilled.
EP 0 244 917 describes a process for producing soluble metal alkoxides from alkoxy alcohols in organic solvents, but no reference is made therein to a process for the production of high-purity, crystalline magnesium hydroxides having fine porosities and uniform crystallinities.
Processes for producing pure magnesium hydroxides are known in the art. For example, GB-A-667,708 suggests a three-stage process wherein the reaction is carried out with watersoluble C1 or C2 alcohol yielding magnesium alcoholate. In the second stage, said alcoholate is substituted for a longer-chain alcohol, the C1 or C2 alcohol being removed by distillation. The resultant magnesium alcoholate is then hydrolysed in stage 3 of said process.
The manufacture of magnesium alkoxy ethers from hydroxy ethers is known per se (see, for instance, U.S. Pat. No. 3,657,361). However, said patent does not teach that high-purity magnesium hydroxides having special characteristics can be obtained by hydrolysis of magnesium alkoxy ether.
Therefore, it was the object of this invention to develop a process for producing magnesium hydroxide having the following features:
The magnesium hydroxide produced according to the invention is required to have high purity, fine porosity, and uniform crystallinity.
The starting materials shall be inexpensive and readily available.
The manufacturing process shall be feasible both continuously and discontinuously.
Surprisingly, it has been found that the problems cited hereinabove can be solved when employing the process described hereinbelow.